I harvested 3 grapes without quality, after squeezing it also broke quality of juice which become ql 2 after i took it out (the same ql as a bucket which i used).
After stacking 5 broken seeds with 5 normal seeds, stack got half quality of the normal seeds so I asume these broken seeds have quality 0.
(character had 36 farming, other 20 grapes I squeezed in wine press was all above 10ql)